Tar is a component of cigarette smoke considered undesirable and attempts are continually being made to deliver lower quantities of tar to the smoker. Conventional procedures have included increased filtration and ventilation. However, only a certain level of filtration can be achieved with conventional filters before the pressure drop across the filter becomes unacceptably high.
Similarly, only a certain level of ventilation can be achieved before the cigarette smoke takes on an unacceptable "airy" taste. Generally, "low tar" cigarettes tend to be unpopular with smokers, since they fail to deliver sufficient flavour in the smoke to satisfy the smoker.
Another problem encountered by smokers is the increasing levels of tar and flavour delivered by a cigarette as it is smoked, sometimes reaching unacceptable levels in the latter puffs.